1. Field of the Invention
This invention relates to a process for the treatment of carbon steel furnace dusts, and other dusts of similar composition, to facilitate their disposal in an environmentally acceptable manner.
2. Review of the Art
Such dusts have been categorized as hazardous materials because of their significant content of heavy metal compounds which can be leached from the dusts if these are used as landfill. A number of hydrometallurgical processes have been proposed or developed for the treatment of these and similar dusts, several of which are described and reviewed in an article, "Hydrometallurgical Treatment Options for Carbon Steel Electric Arc Furnace Dusts", Dreisinger, Peters & Morgan, Proceedings of the Second International Conference on Separation Science and Technology, published by CSCLE, October 1989.
Other processes employing acetic acid leaching are described in Russian Patent No. 1,092,195 and German OLS 2242351. An objective of such processes (other than that of the Russian patent) is to reduce the leachable content of calcium, zinc and other heavy metals in such dusts to levels which permits their dumping, or recycling to the metallurgical process which generated them: the zinc and heavy metal content should preferably be recovered in forms themselves suitable for metallurgical processing for recovery of the metals concerned. The Russian patent is primarily concerned with the recovery of zinc from the dusts.
Both the UBC-Chaparral process and the German patent utilize an acetic acid leach as just one stage in a multiple leach process for treating such dusts. The resulting multiple leach processes are complex, with potential adverse effects upon their economic practicability, and the zinc and other heavy metals are recovered as carbonates or cementation products which, whilst commercially valuable, may be less acceptable to conventional smelters than conventional sulphide concentrates. The Russian patent deliberately sets acetic acid leach conditions such that other heavy metals are not leached, its primary objective being the recovery of zinc oxide from the dusts; it is not intended to remove other heavy metals from the dusts and is ineffectual in that respect.